#include<stdio.h>
#include<math.h>
int main()
{
    int a,b,c;
    scanf("%d%d%d",&a,&b,&c);
    int p=(a+b+c)/2;
    double s=sqrt((double)p*(double)(p-a)*(double)(p-b)*(double)(p-c));
    printf("%.1f",s);
	return 0;
} 
